A resident walks by a section of the border fence between Mexico and the United States on the outskirts of Tijuana, Mexico April 5, 2016. REUTERS/Jorge Duenes

Hundreds of companies have lined up to help build the border wall between America and Mexico, prepping their bids and their prototype designs to submit to the government for selection.

Beginning next week, the Department of Homeland Security’s Customs and Border Protection agency will start accepting the bids.

The awards for initial contracts are expected to be handed out in April.

The border wall was one of President Donald Trump’s key campaign promises. Democrats and amnesty supporters have fought long and hard against the wall’s construction. Mexico, meanwhile, has steadfastly opposed not just the wall, but also Trump’s insistence Mexican taxpayers would pay for it.

In late January, Mexico President Enrique Pena Nieto said in a televised address: “I regret and reject the decision of the U.S. to build the wall.”

He then added, “I have said time and time again, Mexico will not pay for any wall.”

Trump, meanwhile, said U.S. taxpayers may have to foot the initial bill for the building of the wall, but monies would be recouped later from Mexico – even it if meant the funds would have to come from punitive fees or additional taxes on traded goods.

Reuters, citing an internal Department of Homeland Security study, reported a month ago the border wall could cost as much as $21.6 billion, and take three-plus years to build.

That plan called for a three-phase construction operation, with new fencing and walls spanning about 1,250 miles. Currently, about 654 miles of the border are already fortified.

In the coming days, an expected 300 or so companies – some trained in small fencing, others in massive fortress-style walls – will send in their bids for the project.

It’s not clear which type of fencing companies hold the cards.

“There’s really nothing to say at this point [about the types of companies that will win],” said Terry Willis, with Caddell Construction, a company that already contracts with the government for fencing jobs around the world, CNN Money reported. “It’s all very speculative. Once we get the details, we’ll examine whether it’s something we’d move on.”

The border wall construction was put in motion when Trump signed an executive order during his first week in the White House. Congress already had legislation passed years ago that called for the construction of a wall. Legislators, however, need to find and approve the funding.

Trump’s estimated the wall at around $10 billion. But other estimates have put the cost around $25 billion, speculating the costs of materials could rise dramatically in coming months and years.